Magnesium base alloys



Patented Nov. 1, 1932 UNITED STATES PATENT OFFICE JOHN A. GANN Am) FRED L. REYNOLDS, OF MIDLAND, MICHIGAN, ASSIGNOBS TO THE DOW CHEMICAL COMPANY, OF MIDLAND, MICHIGAN, A CORPORATION OF MICHIGAN MAGNESIUM BASE ALLOYS No Drawing.

The present invention relates to improved light weight alloys in which magnesium is the predominating constituent. One object of our invention is to produce magnesium base alloys having a combination of high tensile strength and other mechanical properties with a good resistance to corrosion. Other objects and advantages will appear as the description proceeds.

The commercial. ternary alloys of magnesium developed up to the present time contain at least one of the metals aluminum, manganese, or zinc as an essential alloying ingredient, and as far as we are aware no one has produced or investigated ternary magnesium ase alloys which do not contain these metals.

We have discovered that highly desirable and useful ternary alloys can be made from magnesium by adding thereto both cadmium and tin in relatively small amounts. These alloys have many valuable properties, including the characteristic low specific gravity approaching that of magnesium, which are not only superior to either of the parent binary alloys, e. g. magnesium-cadmium or magnesium-tin, but also in some respects to the ternary alloys having a small percentage of at least one of the metals aluminum, manganese, or zinc as an essential alloying ingredient.

Accordingly, the alloys which are the subject of our invention contain the three metals magnesium, cadmium, and tin, wherein the magnesium content is in excess of about 75 per cent.

These new alloys may be cast, rolled, extruded or otherwise wrought into shape according to the known methods for working magnesium base alloys. Heat treatments known to those skilled in the art of treating magnesium alloys may be applied effectively to these alloys.

The tensile strength of extruded samples of the known binary magnesium-cadmium alloys containing from 1 to 8 per cent cadmium is approximately 31,000 to 34,000 lbs. /sq. in. and that of the known binary magnesium-tin alloys containing from 1 to 8 per cent of tin ranges from 31,000 to 33,000

lbs/sq. in. The corresponding yield points Application filed February 1, 1932. Serial No. 590,301.

(defined as the load in lbs/sq. in. at which the stress-strain curve deviates 0.1 per cent elonation from the modulus line) range from 15,000 to 17 ,500 lbs. /sq. in.forthe magnesiumcadmium binary alloys, and those for the magnesium-tin binary alloys range from 14,000 to 19,000 lbs/sq. in.

The increase in tensile strength and yield point of our new improved ternary alloys is shown by comparing the above values for the parent binary alloys with the corresponding ternary alloys which are specific examples of the alloys coming within the scope of our invention. These alloys, in the extruded condition, have a tensile strength offrom about 31,000 to 38,000 lbs/sq. in. for a given cadmium content between 1 and 4 per cent and a tin content of from 1 to 8 per cent, the balance being substantially magnesium. The yield points corresponding to these compositions vary from 15,000 to 27,000 lbs/sq. in. Thus a marked improvement in. tensile strength and yield point may be obtained over the known binary alloys above mentioned by employing the ternary combination magnesium-cadmium-tin with amounts of tin and cadmium within the limits indicated.

On testing the corrosion resistance of the magnesium-cadmium-tin ternary alloys coming within the scope of this invention by the well known alternate immersion test, we have found as much as 20 times greater resistance to corrosion in 3 per cent salt solution than is exhibited by the well known aluminum containing ternary alloys, such as magnesium-aluminum-cadmium, magnesium-aluminum-tin, and magnesium aluminum zinc, wherein magnesium is present in predominating amount.

Alloys suitable for hammer forging may have a cadmium content preferably of about 2 per cent, while the tin content may be from 4 to 8 per cent, the balance being magnesium. If the alloys are to be press-forged, rolled, or extruded, more cadmium may be introduced and satisfactory alloys for these methods or working may have a cadmium content lying between 1 and 8 per cent. For good casting alloys the cadmium content may be further increased, but not more than 12 per cent nor under 0.5 per cent ispreferably employed; the tin content at the same time may vary from 0.5 to 12 per cent. In some cases the cadmium content of the alloys may exceed that of tin for certain types of forging operations, and for casting such alloys the proportions for tin may be from 8 to 10 per cent and those for cadmium from 4 to 8 per cent.

These alloys may be prepared by the known metallurgical methods for melting and alloying magnesium.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the proportions of the ingredients employed within the limits specified, provided the ingredients stated by any of the following claims or the equivalent of such stated ingredients be employed.

We therefore particularly point out and distinctly claim as our invention 1. As a new product, a magnesium base alloy consisting of from 0.5 to 12 per cent of cadmium and from 0.5 to 12 per cent of tin, the balance being magnesium.

2. As a new product, a magnesium base alloy consisting of from 1 to 4 per cent of cad-- mium and from 1 to 8 per cent of tin, the balance being magnesium.

3. As a new product, a magnesium base allo consisting of approximately 2 per cent 0 cadmium and from 4 to 8 per cent of tin, the balance being magnesium.

4. As a new product, a magnesiumbase alloy containing from 4 to 12 per cent of cadmium and from 0.5 to 12 per cent of tin, the balance being substantially magnesium.

5. As a new product, a magnesium base alloy containing from 4 to 8 per cent of cadmium and from 8 to 10 per cent of tin, the balance being substantially magnesium.

6. As a new product, a ternary magnesiumcadmium-tin alloy wherein the amount of magnesium varies from 84 to 95 per cent, the cadmium from 1 to 8 per cent and the tin from 4 to 8 per cent.

Signed by us this 28 day of January, 1932.

JOHN A. GANN.

FRED L. REYNOLDS. 

